What can I do? The application of the patch has taken all day and has restarted in my attempt to fix it by restarting my pc and GOG Galaxy. Is there a fix for this or will I just have to wait for another full day without even being able to launch other apps because of how disk consuming this is.

I don't know about the current patch, but there was one in the past that just didn't cope.
The download was enormous (causing problems with disk space) and in many cases it did not update at all.

solution: It was faster uninstalling and reinstalling the game than applying that patch.

Your description sounds as if you are facing that exact problem. You didn't update the game for quite some time, did you?

The patch speed depends on your CPU and game drive.

I have never done any patching through GoG Galaxy as I always do the offline, manual way.
I forgot to note a couple patches in my haste to get from patch 1.5 Hotfix 1 to 1.6, but here's the offline patch disk space requirements:

Cyberpunk.2077.Update.v1.05-GOG - requires 104.804 MB of disk space.
Cyberpunk.2077.Update.v1.06-GOG - requires 5958 MB of disk space.
Cyberpunk.2077.Update.v1.1-GOG - requires 13.146 MB of disk space.
Cyberpunk.2077.Update.v1.11-GOG - requires 5996 MB of disk space.
Cyberpunk.2077.Update.v1.12-GOG - requires 260 MB of disk space.
Cyberpunk.2077.Update.v1.2-GOG - requires 381.401 MB of disk space.
Cyberpunk.2077.Update.v1.21-GOG - requires 6874 MB of disk space.
Cyberpunk.2077.Update.v1.22-GOG - requires 6954 MB of disk space.
Cyberpunk.2077.Update.v1.23-GOG - requires 7108 MB of disk space.
Cyberpunk.2077.Update.v1.3-GOG - requires 385.658 MB of disk space.
Cyberpunk.2077.Update.v1.5-GOG - requires 545.132 MB of disk space.
Cyberpunk.2077.Update.v1.5.1-GOG - requires 65.858 MB of disk space.
Cyberpunk.2077.Update.v1.5.2-GOG - requires XXX MB of disk space. (est. ~240 MB)
Cyberpunk.2077.Update.v1.52-GOG - requires XXX MB of disk space. (est. ~12.000 MB)
Cyberpunk.2077.Update.v1.6-GOG - requires 143.588 MB of disk space.
Cyberpunk.2077.Update.v1.61-GOG - requires 14.852 MB of disk space.

The 1.6 patch took about 12 minutes, and the huge 1.5 patch nearly 40 minutes. I don't really count, I just pull up Youtube on another monitor when installing the larger patches.

I got all my games on a 2 TB NVMe SSD. If you're trying to update with a hard drive...yeah, it will take hours if you have many patches to go through.

They MUST be done in sequential order. Only other alternative is to download the newest game files and renstall.

nvm.

Patching through Galaxy was really transparent to me. I have to running in background all the time, so games get patched when needed.

One day I was on 1.6, the next I was playing on 1.61

However, never ever noticed any heavy resource consumption with Galaxy.

Do you have an SSD or an HDD?